1. Field of the Invention
The present invention relates to a camera having a pseudo format and more particularly to an auto focus camera provided with a taking lens having a plurality of discontinuous, alternative focal lengths and a finder with a variable focal length and that its taking range is set according to the finder's field of vision which is varied as the focal length is varied.
2. Description of the Related Art
In the so-called compact camera it has been rather a common practice to have it provided with as taking lens a multi-focal-length lens with which one of a plurality of discontinuous focal lengths can be arbitrarily selected so that the photographer can take a picture through proper selection of the taking range. Also, there are many with their focal length' magnification ratios set high so that a fairly large picture can be taken of an object located far.
Meanwhile, also known is the so-called pseudo zoom camera, which is a camera capable of varying the taking range without using a multi-focal-length lens and a trimming information is imparted to the film at the time of photographing and at the time of printing the range defined by the trimming information only is enlarged instead of the frame of film as a whole so that an effect similar to zoom photography is obtained.
With such a camera whose taking range is variable the taking range which varies according to manipulation of the taking optical system or the trimming information imparted to the film is requited to be accurately shown in the finder to be clearly visible to the photographer. Hence with a camera having a multi-focal-length lens in its taking optical system is often the case that the finder, too, is of a multi-focal-length type having a multi-focal-length optical system with which any one of a plurality of discontinuous focal lengths can be selected arbitrarily.
Meanwhile, as pseudo zoom cameras are proposed those with which indices are shown in the finder at four corners of the varying taking range by the use of liquid crystal display means or alternatively outside the taking range is masked by the use of similar liquid crystal display means and further those having a multi-focal-length finder as mentioned above or a finder having a zoom optical system which allow continuous variation of the focal length.
When it is tried to increase the magnification ratio for the taking optical system's focal length to say 4-fold so as to attain the object of taking a picture of far object as large as possible as described above, the following problems arise concerning the finder for the purpose.
That is, with the pseudo zoom camera whose taking range is shown in the finder by the use of the liquid crystal display means, the image in the taking range in the finder is bound to be extremely small when magnification is high, this resulting in marked lowering of the finder's recognizability. In this respect, a finder of variable focal length such as zoom finder with which the focal length can be varied continuously allows a high degree of recognizability even in a high magnification range. With a finder of this type, however, the finder itself is bound to be rather bulky if high magnification is to be achieved, this resulting in sizable increase of the camera as a whole.
With camera also having auto-focus function, if they are of the phase differential detection type with their focal length detection means being of TTL (Through The Lens) system, a line sensor having CCD (Charge Coupled Device) or the like as photoreceptor element is bound to be located behind the position equivalent to the film surface with optical elements such as a condenser lens and a separator lens for laterally separating the luminous flux having passed through the taking lens arranged in between. Since with this type of camera the proportion of the distance-measuring range (photoreceptor element's light-receiving range) to the photographed range on the film is constant, it means that the proportion of distance-measuring range to the range to be printed is increased when pseudo zoom photography is done at a proper trimming magnification. Hence, this proportion increases with increasing trimming magnification and probability of the number of objects getting into the distance-measuring range increasing becomes higher, this resulting in a higher probability of erroneous distance-measuring as the distances not only to the main object but also to other objects not intended are likely to be measured.
This problem of the probability of erroneous distance-measuring becoming higher is the case not only with cameras of the phase differential detection type but also with those of the contrast detection type and many others of the external light distance-measuring type instead of TTL system.
In order to take a largest possible picture of a far object, there is also proposed to pseudo zoom camera combining the effect of the telephoto photography (long focal length photography) with that of pseudo telephoto photography so as to increase the settable range of pseudo focal length (product of the real focal length and the trimming factor). With such a pseudo zoom camera the taking lens used is a multi-focal-length lens with which any one of a plurality of discontinuous focal lengths is selectable and it is so arranged that the aforementioned trimming information is imparted to the film at the time of photographing.
With this pseudo zoom camera of the multi-focal length type, however, the taking lens' real focal length is combined with a trimming factor selected as follows. When the taking lens used has two alternative focal lengths of 35 mm and 70 mm, it is most efficient if the pseudo focal distance is 35-70 mm when the taking lens' real focal length is 35 mm for the pseudo focal distance can then be set continuously, hence in this case the trimming factor is set at a maximum of 2. The pseudo focal length, therefore, can be set within a range of 70-140 mm when the real focal length is 70 mm, and this means that an overall range of 35-40 mm can be covered.
In such a composition, however, frequent changing of the focal length becomes necessary when photographing is done with the pseudo focal length set in the vicinity of the taking lens' changeover point, this giving cause for noise and/or increased power consumption.
In the example described above this is the case when it is attempted to set the pseudo focal length in the vicinity of 70 mm. When the photographer tries to find the optimum pseudo focal length in the vicinity thereof and after varying the pseudo focal length from 65 mm through 70 mm to 75 mm or so and, unable to find the optimum taking range, tries to bring it again below 70 mm. If this is done, the taking lens' position is changed each time the focal length passes 70 mm. If such an attempt is repeated a number of times, the focal length of the taking lens is changed the same number of times, this giving rise to noise and/or waste of power as described above.